The present invention, in some embodiments thereof, relates to a combination therapy for attaining a stable and long term cell or tissue transplantation.
The use of full-haplotype mismatched haploidentical donors as an alternative source for hematopoietic stem cell transplantation (HSCT) is highly attractive since virtually all patients have a readily available haploidentical family member that can serve as an HSCT donor. Early attempts to avoid fatal graft versus host disease (GVHD) risk and to apply haploidentical rigorously T cell depleted bone marrow transplantation (TDBMT) in leukemia patients revealed that the absence of donor T cells within the graft leads to a high rate of graft rejection, mediated by residual radiotherapy and chemotherapy resistant host-derived T cells (HTC). To overcome this obstacle, a ‘mega dose’ of TDBM cells was contemplated which can overcome this HTC mediated immune barrier and be engrafted successfully even when using fully mismatched murine strain combinations [Bachar-Lustig E et al., Nat. Med. (1995) 1:1268-1273]. Subsequently, it was demonstrated that in humans, as in rodents, CD34+ hematopoietic stem cell dose escalation may be used to overcome genetic barriers, enabling satisfactory survival rates following purified haploidentical HSCT [Reisner Y and Martelli M F. Immunol Today. (1995) 16:437-440 and U.S. Pat. No. 5,806,529].
While the use of a purified ‘mega dose’ of CD34+ HSCT has enabled haploidentical transplantation in leukemia patients, one major drawback, common to all T cell depleted transplants, is the slow recovery rate of the recipient's immune system. This is attributed to extensive immune ablating conditioning protocols prior to transplantation, the low numbers of donor T cells infused within the graft and to the decreased thymic function of adult recipients. Thus, in adult recipients of a haploidentical CD34+ stem cell graft, a significant rate of transplant related mortality (TRM) is caused by opportunistic infections.
Several approaches are being developed to address this challenge. This includes novel modalities to improve thymic function, post-transplant adoptive transfer of anti-viral specific T cells, transfer of partially polyclonal host-non-reactive allo-depleted T cells or transfer of fully polyclonal T cells transfected with inducible suicide genes. An alternative and additional approach to preserve host immunity is the use of reduced intensity conditioning (RIC). This non-myeloablative approach spares a substantial level of host immune cells and thus may reduce TRM by both improving post-transplant immune reconstitution and reducing the toxicity associated with the conditioning agents. Haploidentical transplantation under RIC is even more intricate due to the substantial immunological barrier presented by the surviving host T cells. Recent attempts to overcome this barrier, largely made use of non-T cell depleted grafts, which enable a high rate of engraftment, but in the expanse of increased rates of GVHD. Another approach for applying haploidentical transplantation under RIC uses CD3/CD19 depleted grafts, which not only contain CD34+ stem cells but also CD34 negative progenitors, NK, graft facilitating cells and dendritic cells, however, this too is at the expanse of increased rates of GVHD and TRM.
In the 1970's George Santos demonstrated in rodents that a short course of high-dose cyclophosphamide (CY) soon after bone marrow transplant (BMT) targeted activated donor or host alloreactive T cells [Owens A H Jr and G W. S. Transplantation. (1971) 11:378-382]. Cyclophosphamide was observed to be non-toxic to hematopoietic stem cells because of their high expression of the detoxifying enzyme aldehyde dehydrogenase, and Slavin et al. further demonstrated that administration of high dose cyclophosphamide can reduce GVHD and graft rejection in mice, without adverse effects on stem cell engraftment [Brodsky R A and R J. J. Lancet. (2005) 365:1647-1656]. Clinical trials by the John Hopkins and Fred Hutchinson Cancer Research Center groups, evaluated a non-myeloablative protocol of cyclophosphamide, fludarabine and 2Gy TBI, and post-transplant GVHD prophylaxis with cyclophosphamide (50 mg/kg days +3 and +4), MMF (days +5 to +35) and tacrolimus (days +5 to +180) [Luznik L et al., Biology of blood and marrow transplantation: journal of the American Society for Blood and Marrow Transplantation. (2008) 14:641]. According evident from their teachings, this protocol resulted in a high relapse rate, which was probably due to poor disease debulking by the non-myeloablative conditioning and to lack of GVHD related graft versus leukemia (GVL) effect [Munchel A et al., Pediatric Reports (2011) 3:43-47].
Additional approaches for achieving stable engraftment of allogeneic hematopoietic stem cells have been attempted, some are described in U.S. Patent Application No. 20110110909, U.S. Patent Application No. 20050118142, U.S. Patent Application No. 20070098693, U.S. Pat. Nos. 5,876,692, 5,514,364, 6,217,867, 5,635,156, U.S. Patent Application No. 20060140912, U.S. Patent Application No. 20040005300, U.S. Patent Application No. 20070141027, U.S. Patent Application No. 20030017152, U.S. Patent Application No. 20030165475 and U.S. Patent Application No. 20010009663.